Effect of nitrogen fixation enhancing type SEN1 gene on soybean growth

It is well known that the growth of legumes is greatly affected not only by fertilizer nitrogen but also by fixed nitrogen by symbiosis with rhizobia. We have reported that a polymorphism in SEN1, which is essential for nitrogen fixation in Lotus japonicus, could be used to enhance nitrogen fixation and plant growth. In this study, we examined whether the same strategy could be applied to Glycine max. Sequencing of orthologs of the LjSEN1 gene in 38 soybean cultivars revealed that the polymorphism occurred at Glyma.08g076300. We defined the standard sequence that most of the cultivars retained as Peking type SEN1, and the mutated sequence found in Enrei as Enrei type SEN1. To investigate the effect of genotype differences, we generated near-isogenic lines by crossing Enrei with Fukuyutaka, which has Peking type SEN1, and analyzed their characteristics. The results showed that Enrei type enhanced nitrogen fixation activity and promoted plant growth. Since soybean SEN1 has been reported to be a homolog of vacuolar iron transporter-like protein, we investigated the iron content in the nodules. In the result, the iron content in the nodules of Enrei type was significantly higher than that of Peking type. Iron is known to be present in the active center of nitrogenase, and the high iron content may have contributed to the increased nitrogen fixation activity. These results suggest that Enrei type SEN1 is a nitrogen fixation enhancing gene and that introduction of Enrei type SEN1 may reduce nitrogen fertilizer application and increase yield.